1. Field of the Invention
The present invention relates, in an electronic equipment on which is mounted a circuit capable of acquiring desired characteristics for a specific level of an input signal, to a power control circuit for maintaining the level of a signal outputted by a subsequent stage of the circuit, at a specific value, and to a transmitter having the power control circuit mounted thereon.
2. Description of the Related Art
The CDMA (Code Division Multiple Access) system is being applied to various communication systems because it intrinsically has confidentiality and interference-resistivity and is a multiple access system capable of making effective use of radio frequencies.
On the other hand, the CDMA system is being positively applied in recent years to a mobile communication system because it is able to solve the near-far problem by establishing the technique for realizing the transmitting power control of high responsiveness and accuracy.
FIG. 14 is a block diagram showing an example of the configuration of a transmission part of a radio base station of a mobile communication system to which the CDMA system is applied.
In FIG. 14, a plurality N of power controlling parts 91-1 to 91-N are fed at their individual base band inputs with different base band signals 1 to N, and their outputs are connected with corresponding inputs of a multiplexing part 92. The output of the multiplexing part 92 is connected with a feeding point of an antenna 98 through a D/A converter 93, a modulator 94, a multiplier 95, a variable gain amplifier 96 and an amplifier 97, which are connected in tandem. The output of an oscillator 99 is connected with a carrier input of the modulator 94, and the output of an oscillator 100 is connected with a spreading code input of the multiplier 95. Control terminals of the power controlling parts 91-1 to 91-N and the variable gain amplifier 96 are connected with the corresponding input/output ports of a controlling part 101.
In the transmission part of the configuration, the controlling part 101 forms a wireless zone and a radio channel appropriate for the CDMA system between itself and a mobile station located in the wireless zone, by associating itself with the not-shown receiving part on the basis of a predetermined channel setting procedure. Moreover, the controlling part 101 watches the transmission qualities of the individual radio channels thus formed, by associating itself with the above-described receiving part.
On the other hand, the controlling part 101 varies the gain (FIG. 15(1)) to a value appropriate for the watching result, for such ones of the power controlling parts 91-1 to 91-N as correspond to the individual radio channels of the watching result, to absorb the difference in the transmission loss for each radio channel, as caused by the difference in the relative distances between the individual mobile stations located in the above-described wireless zones and the radio base station and by the change in the distances.
Here, the processing to vary the gain in the base band regions of the power controlling parts 91-1 to 91-N, as described above, will be simply called the xe2x80x9ctransmitting power controlxe2x80x9d.
The multiplexing part 92 thus multiplexes the base band signals, having the level set in the base band regions by the power controlling parts 91-1 to 91-N operating under the controlling part 101, to generate a digital signal indicating the sum of the signals to be transmitted to the above-described plurality of radio channels in the digital region.
The D/A converter 93 converts the digital signal into an analog signal. The modulator 94 generates a primary modulated wave by modulating the carrier signal generated by the oscillator 99, according to the analog signal.
Here, it is assumed for simplicity that the modulation made by the modulator 94 corresponds to a primary modulation appropriate for the direct sequence type of the CDMA system.
The multiplier 95 generates the transmission wave by performing a secondary modulation to multiply the spreading code generated by the oscillator 100 and the above-described primary modulated wave.
The variable gain amplifier 96 performs power amplification (FIG. 15(2)) together with the amplifier 97 to feed the above-described transmission wave to the feeding point of the antenna 98. Here, the gain of the variable gain amplifier 96 is adjusted to a constant value at which the level of the transmission wave takes a predetermined value in the course of the running and maintaining routines.
By sharing the variable gain amplifier 96 and the amplifier 97 for the transmissions of the plurality of radio channels, therefore, the hardware of the radio base station is scaled down, and the level of the transmission wave to be transmitted through the antenna 98 is kept for each channel at the level of eliminating or easing the xe2x80x9cdeterioration in the transmission quality caused by a drastic change or difference of the location of the individual mobile stations located in the wireless zone formed by the radio base stationxe2x80x9d (as will be shortly called the xe2x80x9cnear-far problemxe2x80x9d).
Here in this example of the prior art, in order to solve the near-far problem, the transmitting power control generally has to be made over a dynamic range wider by 40 decibels to 60 decibels than that of the transmitting part appropriate for the TDMA system or the FDMA system.
In order to achieve the desired characteristics for the analog signal fed under the power control made over such wide dynamic range, therefore, not an active modulator to which an active element is applied but a passive modulator composed of only passive element(s) has/have to be applied as the modulator 94.
However, the passive modulator has a wider dynamic range than that of the active modulator (FIG. 16(b)), as shown in FIG. 16(a), but it is constructed mostly of discrete parts so that it has a large physical size.
Of the circuits constructing the passive modulator, moreover, a phase shift circuit for converting the carrier signal generated by the oscillator 99 into two carrier signals crossing each other has a far higher changing rate of phase shift with respect to the temperature than that of an equivalent circuit belonging to the active modulator.
In the example of the prior art, therefore, a temperature compensating circuit for compensating the fluctuation of the phase shift with respect to the temperature has to be mounted together with the modulator 94.
Here, the active modulator has a far lower changing rate of characteristics with respect to the temperature than that of the passive modulator, as illustrated in FIGS. 17(a) and (b), so it can be applied when a desired dynamic range is achieved.
However, the active modulator is unable to realize the above-described wide dynamic range due to the characteristics of the active elements to be applied and by the restrictions on the power supply voltage, so that it is practically hard to apply and cannot always realize an integrated circuit.
On the other hand, with the above-described desired dynamic range wider, the level of the analog signal to be actually inputted to the modulator 94 has a higher possibility of exceeding the range of the appropriate input level at which the upper limit and the lower limit are given, for example, by two thin dotted lines as illustrated in FIG. 15, and at which the above-described desired characteristics are kept.
An object of the invention is to provide a power control circuit and a transmitter having performances maintained stable over a wide dynamic range without any drastic changes in the configuration.
Another object of the invention is to keep the desired characteristics and performances maintained even if the level of an input signal may fluctuate.
Still another object of the invention is to avoid the degradation of performances due to the fluctuation or deviation of the characteristics of components.
A further object of the invention is to obtain a signal of a satisfactory SN ratio and a desired level at an output terminal and stably maintain the level of reliability and performance irrespective of the level of the input signal.
A further object of the invention is to ease the restrictions on the packaging and component orientation.
A further object of the invention is to reduce the manufacturing, maintenance and running cost and to enhance the overall reliability without drastically complicating the configuration or enlarging the scale of the hardware.
The above-specified objects are achieved by a power control circuit comprising: measuring means for measuring the level Li of an input signal; level variant means for amplifying the input signal with a first gain G1 and feeding it to a circuit for making a desired response when fed with a signal at a predetermined level Ls; level adjustment means for amplifying an output signal obtained as a response of the circuit, with a second gain G2; and controlling means for setting the first gain G1 to a ratio between the predetermined level Ls and the level Li measured by the measuring means and setting the second gain G2 to a ratio between a level Lt of an output signal to be obtained at the output terminal of the level adjustment means and a product of the predetermined level Ls and a gain g of the circuit in a condition for making the desired response.
In this power control circuit, at the individual stages from the input terminal of the level variant means through the circuit to the output terminal of the level adjustment means, the level diagram is distributed while maintaining the condition for meeting the requirement for the circuit to make the desired response, and the output signal at the desired level Lt is obtained at the output terminal of the level adjustment means even if the level of the input signal fluctuates.
Therefore, even if there is a wide range for the level of the input signal to fluctuate, the desired characteristics and performances are maintained at a highly accurate level.
On the other hand, the above-described objects are achieved by a power control circuit comprising: measuring means for measuring a level Li of a specific input signal to meet the requirement for a circuit making a desired response to make the desired response, among a plurality N of input signals fed in parallel when fed with a signal at a specific level Ls; combining means for combining the plurality of input signals to generate a single input signal; level variant means for amplifying the single input signal which is generated by the combining means and is to be fed to the circuit, at a stage prior or subsequent to the combining means with a first gain G1; level adjustment means for amplifying an output signal, obtained as a response of the circuit, with a second gain G2; and controlling means for setting the first gain G1 to a ratio between the specific level Ls and the level Li measured by the measuring means and setting the second gain G2 to a ratio between a level Lt of an output signal to be obtained at the output terminal of the level adjustment means and a product of the specific level Ls and a gain g of the circuit in a condition for the desired response.
In this power control circuit, at the individual stages from the input terminal of the combining means through the level variant means and the circuit to the output terminal of the level adjustment means, the level diagram is distributed while maintaining the condition for meeting the requirement for the circuit to make the desired response, and the output signal at the desired level Lt is obtained at the output terminal of the level adjustment means even if the level of the input signal fluctuates.
Therefore, even if there is a range for the level of the input signal to fluctuate, the desired characteristics and performances are maintained at a highly accurate level.
On the other hand, the above-described objects are achieved by a transmitter comprising: measuring means for measuring the level Li of an input signal; level variant means for amplifying the input signal with a first gain G1; a modulator for generating a modulated wave by modulating a carrier signal in accordance with an input signal fed through the level variant means, the modulator having a desired characteristic when fed with a signal at a predetermined level Ls; level adjustment means for generating a transmission wave to be sent to a transmission channel by amplifying the modulated wave generated by the modulator, with a second gain G2; and controlling means for setting the first gain G1 to a ratio between the predetermined level Ls and the level Li measured by the measuring means and setting the second gain G2 to a ratio between a level Lt of a transmission wave to be obtained at the output terminal of the level adjustment means and a product of the predetermined level Ls and a gain g of the modulator in a condition for the making desired response.
In this transmitter, at the individual stages from the input terminal of the level variant means through the modulator to the output terminal of the level adjustment means, the level diagram is distributed while maintaining the condition for meeting the requirement for the modulator to make the desired response, and the output signal at the desired level Lt is obtained at the output terminal of the level adjustment means even if the level of the input signal fluctuates.
Therefore, even if there is a range for the level of the input signal to fluctuate, the desired characteristics and performances are maintained at a highly accurate level.
Moreover, the above-described objects are achieved by a transmitter comprising: combining means for combining a plurality of input signals fed in parallel and generating a single input signal; a modulator for generating a modulated wave by modulating a carrier signal in accordance with a single input signal inputted, the modulator having a desired characteristic when the level of the single input signal is at a predetermined level Ls; level variant means for amplifying the single input signal to be fed to the modulator through the combining means, at a stage prior or subsequent to the combining means with a first gain G1; measuring means for measuring the level of the plurality N of input signals; level adjustment means for generating a transmission wave to be sent out to a transmission channel by amplifying the modulated wave generated by the modulator, with a second gain G2; and controlling means for reducing the first gain G1 of the level variant means and enlarging the second gain G2 of the level adjustment means, when the level of at least one input signals exceeds a threshold value in the measuring means.
In this transmitter, at the individual stages from the input terminal of the combining means through the level variant means and the modulator to the output terminal of the level adjustment means, the level diagram kept in a condition that the degradation of the characteristics of the modulator is reduced or suppressed due to the rise in the level of the input signal.
Therefore, even when the level of the input signal rises, the desired characteristics and performances are maintained at a highly accurate level.
Moreover, the above-described objects are achieved by a power control circuit, in which the difference in the response time between the prior stage and the subsequent stage of the circuit is suppressed, and a transmitter provided with a modulator as the circuit.
In the control circuit and transmitter, the excess and deficiency of the gain are avoided, as could otherwise transiently occur at the above-described prior and/or subsequent stages.
On the other hand, the above-described objects are achieved by a power control circuit for making a feed-back control to maintain the level of the signal obtained at the output terminal of the subsequent stage of the circuit, at a desired value, and a transmitter provided with a modulator as the circuit.
In the power control circuit and transmitter, the degradation in the performance are avoided due to the fluctuation of characteristics and the deviation of the circuit and the prior stage of the circuit.
Moreover, the above-described objects are achieved by a power control circuit for keeping the gain of the prior stage of the circuit at the value for the maximum SN ratio of an output signal obtained at the output terminal of the circuit, and a transmitter provided with a modulator as the circuit.
In these power control circuit and transmitter, the level of the reliability and performance are maintained stable irrespective of the number of input signals fed in parallel with the circuit and the level of the input signals.
On the other hand, the above-described objects are achieved by a power control circuit, in which the gain of a subsequent stage of the circuit is fed as instantaneous values of multiple-valued analog signals to the subsequent stage and to which the gains fed as the instantaneous values are held and applied cyclically in the order of time series, and a transmitter provided with a modulator as the circuit.
In the power control circuit and transmitter, with the number of gains expressed as the multiple-values larger, the desired number of signal lines is reduced, and the restrictions on the packaging and component orientation are eased.
Moreover, the above-described objects are achieved by a power control circuit, in which the gain of the prior stage of the circuit is varied on the basis of the hysteresis appropriate for the history of the level of the signal actually inputted, and a transmitter provided with a modulator as the circuit.
In the power control circuit and transmitter, even if the level of the input signal fed to the prior stage of the circuit frequently fluctuates, the level of the input signal fed to the circuit is maintained at a highly accurate and stable level at the value for the circuit to make a predetermined response, so that the performance is maintained stable.
Here, further objects and features of the present invention will be clarified by the following detailed description to be made with reference to the accompanying drawings.